1. Field of the Invention
The present invention relates to a surface-emitting device and a liquid crystal display device.
2. Description of the Related Art
Hitherto, in reflective liquid crystal display devices that produce display with ambient light used as a light source, the visibility of the display extremely decreases in an environment in which ambient light is insufficient, for example, when used in a dark place, because the brightness depends on the amount of ambient light. Accordingly, a liquid crystal display device has been proposed in which a front light (surface-emitting device) serving as an auxiliary light source is placed in the front of a reflective liquid crystal display unit (liquid crystal display element). The liquid crystal display device having the front light operates as a normal reflective liquid crystal display device in an environment in which ambient light is sufficient, for example, outdoors in the daytime, and illuminates the front light as the light source, as necessary. FIG. 6 shows an example of such a liquid crystal display device in which a front light is placed in the front of a liquid crystal display element. A liquid crystal display device 100 shown in FIG. 6 includes a liquid crystal display unit 120, and a front light 110. The front light 110 is placed in the front of (on the upper surface in FIG. 6) of the liquid crystal display unit 120 so that a light guide panel 112 is disposed in a display region of the liquid crystal display unit 120.
The front light 110 includes a flat light guide panel 112 formed by injection-molding a transparent acrylic resin or the like, and a bar light source 113 disposed at an end of the light guide panel 112. A light-source cover 115 having an angular-U profile and made of a metal plate is mounted from the side of the bar light source 113. That is, the light-source cover 115 stores the bar light source 113 therein, and grasps the ends of the upper and lower surfaces of the light guide panel 112 on the side of the bar light source 113 by the inner surface at its open leading end, thereby supporting the light guide panel 112 and the bar light source 113 at predetermined positions. A reflecting film (not shown) made of a silver thin film or the like is formed on the inner surface of the light-source cover 115 so as to return light, which is emitted toward the inner surface of the light-source cover 115 without entering the light guide panel 112, to a light guide member 113a for utilization. The lower surface of the light guide panel 112 (on the side of the liquid crystal display unit 120) serves as an emergent surface from which light emerges, and a surface opposite from the emergent surface (upper surface of the light guide panel 112) serves as a prism surface 112c on which wedge-shaped grooves 114 are alternately and periodically arranged so as to change the direction of light propagating inside the light guide panel 112.
The bar light source 113 includes a bar-shaped light guide member 113a, and LEDs (Light Emitting Diodes) 113b disposed at both ends thereof so as to serve as light emitting elements. Light emitted from the LEDs 113b is guided to an end face 112a of the light guide panel 112 by the light guide member 113a, and enters the light guide panel 112 through the end face 112a. 
The liquid crystal display unit 120 is of a reflective type, and produces display by reflecting light incident from the front light 110 by a built-in or externally mounted reflecting plate. The liquid crystal display device 100 having the above configuration produces normal reflective display by reflecting external light in an environment in which external light is sufficient, and produces display by reflecting light from the front light 110 serving as the light source in a dark place in which external light is not obtained.
In the liquid crystal display device 100 having the above configuration, however, a phenomenon in which the brightness of the front light 110 partially decreased sometimes occurred in acceleration tests in which heating and cooling were periodically repeated. The present inventors and the like made examinations on this problem, and found that the decrease of the brightness was caused by the displacement of the light guide panel 112 and the light guide member 113a. 
FIG. 7 is a plan view showing the optical path of the front light 110 shown in FIG. 6. As shown in FIG. 7, a surface of the light guide member 113a of the bar light source 113 opposite from the light guide panel 112 serves as a prism surface 118, and light incident from the LEDs 113b on the light guide member 113a is reflected by the prism surface 118, and is emitted toward the light guide panel 112. Since the propagating direction of the light reflected by the prism surface 118 is limited to a narrow range in the front light 110 having such a structure, the position of the light guide panel 112 relative to the light guide member 113a of the bar light source 113 must be exactly adjusted, in particular, in the widthwise direction of the light guide panel 112, in order to uniformly direct the light into the light guide panel 112. For example, as shown in FIG. 7, when the light guide panel 112 is displaced to the right in the figure, the amount of light at a right edge 116 of the light guide panel 112 partially decreases, and the amount of emergent light is prone to be nonuniform in the plane. This partially decreases the visibility of the liquid crystal display device 100.
Since the bar light source 113 and the light guide panel 112 are fixed by mounting the light-source cover 115 having an angular-U profile to the end of the bar light source 113 in the liquid crystal display device 100, as described above, the light guide panel 112 is grasped by the inner side of the light-source cover 115. Since the light guide panel 112 is clamped by a wide inner surface of the light-source cover 115 in such a structure, the wide inner surface of the light-source cover 115 receives expansion and contraction of the reflecting film formed on the inner surface of the light-source cover 115, and the light guide panel 112 is prone to displacement.
Accordingly, an object of the present invention is to provide a reliable surface-emitting device in which a bar light source and a light guide panel can be placed and maintained in precise positions.
Another object of the present invention is to provide a reliable liquid crystal display device in which a surface-emitting device and a liquid crystal display element can be maintained in precise positions.
In order to achieve the above objects, according to an aspect, the present invention provides a surface-emitting device including a bar-shaped light source, and a light guide panel in which light from the light source is introduced from an end face and is emitted from an emergent surface, wherein the light source is supported at an end of the light guide panel by a cover member disposed so as to cover the light source and the end of the light guide panel, projecting pieces are formed at both ends of the cover member so as to clamp the end of the light guide panel from both sides in the widthwise direction, and the light guide panel is positioned in the widthwise direction by the projecting pieces.
In such a configuration, since the light guide panel can be precisely positioned in the widthwise direction by the projecting pieces formed at both ends of the cover member, the light guide panel and the light source are rarely displaced, and the reliability of the surface-emitting device can be increased.
Preferably, projecting pieces contain first portions that project in the widthwise direction of the light guide panel and second portions that extend from the first portions along the lengthwise direction of the light guide panel, and the distance between the projecting pieces is substantially equal to the width of the light guide panel. In such a structure, the movement of the light guide panel in the widthwise direction is limited by the projecting pieces disposed on both sides thereof, and the light source and the light guide panel can be fixed so that they are less prone to displacement.
According to another aspect, the present invention provides a surface-emitting device including a bar-shaped light source, and a light guide panel in which light from the light source is introduced from an end face and is emitted from an emergent surface, wherein the light source is supported at an end of the light guide panel by a cover member disposed so as to cover the light source and the end of the light guide panel, protuberances are formed on the inner surface of the cover member so as to be in contact with the end of the light guide panel, and the cover member clamps the end of the light guide panel via the protuberances.
Since the cover member for fixing the light guide panel grasps the light guide panel via the protuberances formed on the inner surface thereof, the contact area between the light guide panel and the cover member can be made smaller than in the conventional configuration in which the cover member fixes the light guide panel by the inner surface or edge thereof, and therefore, the changes in size of the light-source cover and the light guide panel due to expansion and contraction rarely affect each other. Consequently, the light guide panel and the light source will not be displaced by heating and cooling, and the reliability of the surface-emitting device can be increased.
According to a further aspect, the present invention provides a surface-emitting device including a bar-shaped light source, and a light guide panel in which light from the light source is introduced from an end face and is emitted from an emergent surface, wherein the light source is supported at an end of the light guide panel by a cover member disposed so as to cover the light source and a part of the light guide panel, protuberances are formed on the inner surface of the cover member so as to be in contact with the end of the light guide panel, the cover member clamps and supports the end of the light guide panel via the protuberances, projecting pieces for clamping the end of the light guide panel from both sides in the widthwise direction are formed at both ends of the cover member, and the light guide panel is positioned in the widthwise direction by the projecting pieces.
That is, this surface-emitting device has the structure for supporting the light guide panel by the protuberances and the structure for positioning the light guide panel by the projecting pieces extending at both ends of the light source. Therefore, this configuration makes it possible to achieve a more reliable surface-emitting device in which the light guide panel and the light source are not displaced by expansion and contraction of the light guide panel and the light-source cover due to heating and cooling.
The projecting pieces may serve as fitting portions for fixing the surface-emitting device to a housing. This allows the surface-emitting device to be easily and precisely fixed to an electronic device, and enhances the working efficiency during production. Moreover, since the light source and the light guide panel can be precisely positioned by the projecting pieces, and are rarely displaced, as described above, for example, the light guide panel and a display element placed on the rear side thereof can also be precisely positioned by reliably fixing the cover member to the housing by the fitting portions.
The projecting pieces may respectively have base portions extending from both ends of the cover member in the thickness direction of the light guide panel, fitting plates extending from the leading ends of the base portions in the lengthwise direction of the light guide panel, retaining portions projecting from the outer edges of the fitting plates and bent upward at connecting portions to the fitting plates, and retaining projections bent upward at the leading ends of the fitting plates.
That is, the surface-emitting device can be easily fixed to the housing by forming the retaining portions for fixing on the outer sides of the fitting plates extending in the lengthwise direction of the light guide panel. By forming the retaining projections at the leading ends of the fitting plates, the movement of the surface-emitting device in the lengthwise direction of the light guide panel can be limited, the surface-emitting device can be precisely positioned, and the position thereof is rarely displaced.
Preferably, a reflecting film for reflecting light from the light source is formed on the rear side of the light-source cover. In this case, light incident on the inner surface of the light-source cover can be reflected to reduce the light loss by the light-source cover, and to enhance the utilization efficiency of the light source.
According to a further aspect, the present invention provides a liquid crystal display device including any of the above-described surface-emitting devices that is disposed in the front of a liquid crystal display element. That is, the adoption of the above highly reliable surface-emitting device can achieve a liquid crystal display device in which the brightness is rarely decreased by heating and cooling, and high visibility is ensured for a long period.
According to a still further aspect, the present invention provides a liquid crystal display device including a surface-emitting device in which projecting pieces are formed as fitting portions in the above-described cover member, a liquid crystal display element placed on an emergent side of the surface-emitting device, and a housing for supporting the surface-emitting device and the liquid crystal display element, wherein hook-shaped retaining members formed in the housing are engaged with the projecting pieces of the cover member in the surface-emitting device so that the surface-emitting device, the liquid crystal display element, and the housing are fixedly combined. This allows the surface-emitting device to be easily and precisely fixed to the housing via the fitting portions.
Preferably, the length of fitting plates of the projecting pieces and the width of the retaining members are substantially equal to each other. In this case, it is more difficult for the position of the surface-emitting device to be displaced from the housing. This is because the movement of the surface-emitting device in the lengthwise direction of the light guide panel relative to the retaining members of the housing is limited by retaining projections formed in the fitting portions. The movements of the surface-emitting device in the widthwise direction and the thickness direction of the light guide panel are limited by engaging the retaining members with retaining portions formed on the outer sides of the fitting portions. Consequently, it is possible to minimize the displacement of the surface-emitting device from the housing, and to increase the reliability of the liquid crystal display device.
Further objects, features, and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.